Dimensional stability of Superinvar

Attention is called to new thermal expansion measurements on temporally stable Superinvar. The measurements indicate that its thermal expansivity vs temperature is more desirable than has been suggested by earlier measurements (Berthold et al., 1976). It is pointed out that at approximately 47 C, the thermal expansion coefficient is zero; however, the coefficient increases rapidly as the temperature departs from 47 C. A second zero-crossing of the expansivity is found at -21 C. The magnitude of negative expansivity between -21 C and 45 C remains bounded and small. No disruptive and reversible phase transition is found at temperatures down to -26 C.